1. Field of the Invention
The present invention relates to an insitu hard mask open strategy which is performed before carrying out a metal etch. The present invention is particularly suited for the processing of 300 mm silicon wafers.
Plasma assisted dry etching processes are widely used in the field of microelectronics and micromechanics. When features having a high aspect ratio are to be patterned as well as when rather etch resistant layers have to be patterned, very high demands must be met by the etching mask. In most cases photoresist masks are insufficient in order to achieve the necessary etching selectivities. In these cases so called hard masks are used, the patterning of which again can become a severe problem.
2. Summary of the Invention
It is accordingly an object of the invention to provide a method for etching a hard mask layer and a metal layer that overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which achieves a better control of the critical dimensions (CD). Especially it is an object to reduce the CD in an insitu hard mask open step.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for etching a hard mask layer containing silicon oxide, silicon nitride or silicon oxynitride, and for etching at least one metal layer containing aluminum. The method includes providing a substrate having thereon the metal layer, the hard mask layer, and a patterned photoresist layer overlying the hard mask layer in a plasma processing chamber. The hard mask layer is etched using a plasma etching process using an etchant source gas formed of a fluorine containing gas and oxygen. A flow rate of the oxygen is 5 to 10% based on a flow rate of the fluorine containing gas. The metal layer is etched in the plasma processing chamber after the hard mask layer has been etched. A plasma clean step is performed to clean the walls of the plasma processing chamber using an a cleaning gas formed of one of an inert gas and oxygen, after the metal layer has been etched. Finally, the patterned photoresist layer is subsequently removed from the hard mask layer.
As the inventors of the present invention found, in an insitu hard mask open process the CD of metal lines can be advantageously reduced if a small amount of oxygen is added to the etchant source gas used for etching the hard mask.
In particular, it was found that the metal etch step provides almost perpendicular walls whereas a taper is mainly induced by the hard mask opening step. More specifically, when performing any anisotropic plasma etching process, the etchant source gas will also attack the photoresist layer whereby polymers will be produced which will then be deposited at the sidewalls of the trench. For example, during the metal etch step, a thin polymeric film will be formed on the trench walls so as to prevent the walls from being further etched, whereas the thin polymeric layer deposited on the trench bottom will be destroyed by ion bombardment during the plasma etching process. In contrast, due to the specific plasma conditions during the hard mask open step, the polymeric layer will be deposited onto the trench walls so as to produce a tapered shape.
By adding a small amount of oxygen, for example 5 to 10 sccm (cubic centimeters per minute under standard conditions) if 100 sccm of a fluorine containing gas are fed, the tapered shape can be avoided, whereby a vertical etching profile is achieved. Consequently, the CD can be better controlled and further be reduced.
Moreover, the present invention provides a method for patterning the metal layer stack containing at least one metal layer on a substrate, contains the steps of the method according as defined above, and the step of etching the at least one metal layer in the plasma processing chamber in another subsequent plasma etching process. Both etching processes are performed within the same plasma processing chamber preferably without breaking the vacuum. The plasma etching process for etching the metal layer uses a different etch gas composition when compared to the hard mask etch step.
A problem which may arise when the insitu etching process for etching the hard mask layer and the metal stack including a layer containing aluminum is performed a plurality of times so as to process several wafers is that the aluminum etched will be deposited on the plasma processing chamber walls. If thereafter a new wafer is introduced into the plasma processing chamber and a hard mask etching step using oxygen is performed, the deposited aluminum will react with the oxygen to form aluminum oxide which is very brittle and, thus, will peel off the plasma processing chamber walls so as to fall onto the wafer and cause unwanted impurities on the wafer surface.
This problem can be solved if the plasma processing chamber is cleaned by an additional plasma cleaning step using for example an inert gas or oxygen as a cleaning gas, the cleaning step being performed after the metal etch step.
Using the plasma cleaning step, all the polymers and all the aluminum which have been deposited on the plasma processing chamber walls during the metal etch step will be removed before the next oxygen containing hard mask open step of the next wafer will start.
In summary, the present invention provides the now described advantages. The hard mask layer and the metal stack are etched insitu, that is in one single plasma processing chamber and without breaking the vacuum lock. Accordingly, only one plasma etching tool and only one wet cleaning device are necessary. Consequently, processing cost can be reduced. Moreover, since the vacuum is maintained and the wafer need not be transferred from one plasma processing chamber to another, the processing time can be considerably reduced.
Furthermore, the tapered etching profile in the hard mask layer is avoided. Thus, vertical walls can be etched in the hard mask layer and the metal layer stack, whereby the CD can be remarkably reduced and be better controlled. In particular, the CD defined in the photoresist layer corresponds to the CD etched into the metal layer stack.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for etching a hard mask layer and a metal layer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.